1. Technical Field
The present invention pertains to the field of wireless communication. More particularly, the present invention pertains to the random access procedure that a User Equipment (UE) (wireless communication terminal) follows for (among other uses) initial network access.
2. Discussion of Related Art
The evolved UTRA (E-UTRA or evolved UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access) network architecture includes a radio access network (providing UEs access to a core network of a cellular communication system) where the radio resources are divided into blocks of time (sub-frames) and frequency (frequency blocks). In the uplink, these blocks are used either for what is called here the Shared CHannel (SCH) or the contention-based Random Access CHannel (RACH). (The designation SCH is used here only to indicate uplink radio resources from which a base station can allocate a share for each individual UE, not any particular channel that may be designated by the acronym SCH.) The E-UTRA network includes entities that are called here base stations, and are elsewhere sometimes called Node-Bs, or eNBs. A base station of an E-UTRA network allocates SCH resources for UEs and RACH is used by the UEs to access the network or request SCH resources (or possibly to communicate a small amount of user data in some networks under some circumstances). RACH is also used in networks other than E-UTRA type radio network. RACH is in general a contention-based resource (as opposed to a shared resource) used by UEs to access a radio access network typically for initial access and bursty data transmission.
In the prior art, the random access procedure is used (i.e. RACH is used or an analogous contention-based resource) when a UE needs to transmit user traffic (voice or data) or send a synchronization burst but the UE does not have an allocation of system resources on SCH. The UE may want to perform initial network access, make a location area update, move from the idle mode to the active state, or request capacity while in the active state. The random access procedure ends in an E-UTRA network when the radio access network gives the UE a timing advance value (to compensate for the time between sending a message to the radio access network and the latter receiving the message, and vice versa) and an allocation on SCH (for use as a traffic channel for sending voice or user data to the radio access network).
The problem is to design a random access procedure that provides good coverage and low delay, with minimum use of resources.
The prior art teaches transmitting the random access message (over RACH) on a constant frequency band. It can be advantageous to use a non-constant frequency band. In addition, it can be advantageous to use HARQ (hybrid automatic repeat request processing) in connection with the random access procedure.
The invention can involve what is called here a temporary cell specific address, and now in the art sometimes called a C-RNTI (Cell Radio Network Temporary Identity). The temporary cell specific address/C-RNTI is shorter (e.g. 16 bits) than other unique identifiers such as TMSI (temporary mobile subscriber identifier), IMSI (international mobile subscriber identity), and IMEI (international mobile equipment identity), and so can be used more easily. All the resource allocations are made using the temporary cell specific address (to identity the receiver of the resources). A UE can receive a temporary cell specific address when it first establishes communication with a cell.